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Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Amplitudes of stellar oscillations: the implications for asteroseismology.
There are no good predictions for the amplitudes expected fromsolar-like oscillations in other stars. In the absence of a definitivemodel for convection, which is thought to be the mechanism that excitesthese oscillations, the amplitudes for both velocity and luminositymeasurements must be estimated by scaling from the Sun. In the case ofluminosity measurements, even this is difficult because of disagreementover the solar amplitude. This last point has lead us to investigatewhether the luminosity amplitude of oscillations δL/L can bederived from the velocity amplitude (v_osc_). Using linear theory andobservational data, we show that p-mode oscillations in a large sampleof pulsating stars satisfy (δL/L)_bol_{prop.to} v_osc_/T_eff_.Using this relationship, together with the best estimate ofv_osc_,sun_=(23.4+/-1.4)cm/s, we estimate the luminosityamplitude of solar oscillations at 550nm to beδL/L=(4.7+/-0.3)ppm. Next we discuss how to scale the amplitude ofsolar-like (i.e., convectively-powered) oscillations from the Sun toother stars. The only predictions come from model calculations byChristensen-Dalsgaard & Frandsen (1983, Sol. Phys. 82, 469).However, their grid of stellar models is not dense enough to allowamplitude predictions for an arbitrary star. Nevertheless, althoughconvective theory is complicated, we might expect that the generalproperties of convection - including oscillation amplitudes - shouldchange smoothly through the colour-magnitude diagram. Indeed, we findthat the velocity amplitudes predicted by the model calculations arewell fitted by the relation v_osc_{prop.to}L/M. These two relationsallow us to predict both the velocity and luminosity amplitudes ofsolar-like oscillations in any given star. We compare these predictionswith published observations and evaluate claims for detections that haveappeared in the literature. We argue that there is not yet good evidencefor solar-like oscillations in any star except the Sun. For solar-typestars (e.g., α Cen A and β Hyi), observations have not yetreached sufficient sensitivity to detect the amplitudes we predict. Forsome F-type stars, namely Procyon and several members of M67, detectionsensitivities 30-40% below the predicted amplitudes have been achieved.We conclude that these stars must oscillate with amplitudes less thanhas generally been assumed.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| High-precision time-resolved CCD photometry
High-precision time-resolved photometry and detection of low-amplitudestellar oscillations are limited in precision by many factors. The noiseterms for a typical time-series observation contain observational noiseand errors as well as instrumental noise and reduction noise. This paperdescribes some of the problems related to high-precision photometry,especially focusing on CCD photometry both on focused stars (in semi-and noncrowded fields) and defocused field stars. It is shown thatatmospheric transparency variations and instrumental drift are the mainnoise sources at low frequencies (below 1-2 mHz), and that CCDphotometry is the best way of doing differential measurements in orderto detect oscillations at low frequencies. The theoretical descriptionof noise and problems in high-precision photometry is compared with CCDtime-series observations in a noncrowded test field observed with theDanish 1.5-m telescope at ESO La Silla, Chile in 1990. In addition,observations of defocused double stars observed with the Nordic OpticalTelescope in 1991 are described.
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| Rapid photometry of the Delta Scuti variable 63 Herculis and of the F 2V star HD 155543 - Observations and analysis of the time series
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&A...246...71B&db_key=AST
| Stellar Astrophysics at the I.A.C. 1979-1989
Not Available
| Detection of acoustic oscillations in the F2 V star HD 155543
Results are presented on an analysis of rapid photometric data of the F2V star HD 155543, obtained simultaneously from the Observatorio delTeide (Spain) and the Observatorio de San Pedro Martir (Mexico) duringMay-June, 1987. Strong evidence was found of the presence in this starof acoustic p-mode spectrum; when performing a squared amplitude of theamplitude spectrum for several frequency (nu) intervals, a Delta nu(0) =97.6 + or - 0.6 microHz was found in the frequency range 2-2.2.8 mHz.Several theoretical models compatible with the luminosity and theeffective temperature of the star were computed, and their p-modeeigenfrequencies were obtained. It is found that only models with massesfrom 1.4-solar-mass zero-age main-sequence star to 1.3-solar-mass middleaged star yield values of Delta nu(0) that agree with observations.
| HD 154973, a New Short Period Variable Star
Not Available
| The fourth meridian catalog of Besancon Observatory
The catalog presented gives differential meridian positions for 670F-type stars between plus 15 and plus 45 deg declination. The positionsare reduced to the equinox of 1950.0 without proper motions; 333 FK4stars were used as reference stars. A minimum of three and an average offive transits of each program star were observed photoelectrically usinga Gautier transit circle and a Hog grid. The internal accuracy ofindividual measurements is shown to range from 0.013 sec in rightascension and 0.30 arcsec in declination for brighter stars under betterobserving conditions to 0.020 sec in right ascension and 0.38 arcsec indeclination for fainter stars under worse conditions. The standarderrors were applied to compute weighted mean positions, mean epochs, andunweighted means for the program stars. Mean corrections for 283 FK4stars are also provided.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 17h11m16.92s |
| סירוב: | +24°15'08.7" |
| גודל גלוי: | 6.945 |
| מרחק: | 83.963 פארסק |
| תנועה נכונה: | -13 |
| תנועה נכונה: | 28.8 |
| B-T magnitude: | 7.399 |
| V-T magnitude: | 6.983 |
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